DMOS devices are "double diffused" MOS (metal oxide semiconductor) transistor devices. A DMOS device is characterized by a source region and a backgate region, which are diffused at the same time. The transistor channel is formed by the difference in the two diffusions, rather than by separate implantation. DMOS devices have the advantage of decreasing the length of the channel, thereby providing low-power dissipation and high-speed capability.
DMOS devices may have either lateral or vertical configurations. A DMOS device having a lateral configuration (referred to herein as an LDMOS), has its source and drain at the surface of the semiconductor wafer. Thus, the current is lateral.
In general, desired characteristics of an LDMOS are a high breakdown voltage, BV, and a low specific on-resistance (Rsp). For many applications, it would also be desirable to have an LDMOS that provides electrostatic discharge (ESD) protection. Examples of such applications are print head drivers for printers and electronic braking systems for automobiles.
Existing approaches to ESD protection for LDMOS devices are based on the addition of a protection device to the LDMOS circuit. The protection device is often larger than the LDMOS device being protected.